Men and women differ from each other in peace, so it should come as no surprise that they’ll likely differ in combat, as well.

The Pentagonannounced Thursday that virtually all ground-combat slots will be opening up to women over the next several years. “They’re fighting and they’re dying together, and the time has come for our policies to recognize that reality,” Defense Secretary Leon Panetta said shortly before signing an order lifting a 1994 Pentagon rule on women serving in close-combat positions, largely in infantry and armored units. All military jobs are now open to women unless the services petition that certain billets be closed to them.

Given that ground-combat-breaking change, it’s worth checking out the Pentagon’s own data to see how military women compare with military men.

Males are more aggressive, which can be beneficial in combat. But that trait also leads to more accidents and injuries, up to and including eye injuries (men in the military have twice as many as women) and suicide (men account for about 95% of military suicides). Women are more nurturing, and their most basic form of nurturing – motherhood – accounts for 58% of hospitalizations among active-duty female troops. But they also crash and kill themselves much less often. Yet even once pregnancy and delivery hospitalizations are removed from the equation, female troops are hospitalized at a rate 30% higher than their male counterparts.

The average woman doesn’t have the same upper-body strength as the average man. “From 1970 to the late 1990s, the military services, especially the Army, conducted numerous tests to determine whether the physiological differences between men and women in upper-body strength, stamina, endurance, speed, and coordination were genetically determined or the product of a less active culture among women and, therefore, subject to change through proper conditioning programs,” a 2004 Army study said. “Test results varied widely except in the case of upper-body strength, which, it was generally agreed, seldom reached the male level among females.”

None of these things, of course, are show-stoppers. But the military is always seeking the healthiest, readiest-to-go force as possible, so such gender-different details matter.

In a perfect world, every U.S. soldier would be an asexual brute with a stunningly high IQ who doesn’t eat much, is adept at following orders and leery of challenging authority.

Given that such a creature has never existed, the nation builds its military one compromise at a time.

A pretty good indicator of how women might fare in or near combat is to review the data on medical evacuations from the nation’s two post-9/11 theaters of war. From January 2003 to December 2011, 50,634 troops had to be flown out of Afghanistan and Iraq for medical reasons — 44,258 men and 6,376 women. While women have accounted for about 10% of the U.S. forces deployed into the post-9/11 wars, they represented less than 13% of those medically evacuated – pretty close to their share of the force (battle injuries represented only about 15% of the total).

dod / medical surveillance monthly report

Integrating women into the combat arms – primarily infantry, armor and artillery – is going to be a balancing act. Standards must be met, but there will be pressure to ensure enough women qualify so there’s not only one or two in a 150-troop company.

There are women in the ranks who are stronger than some men in the ranks. So long as standards are properly set, and enforced, these differences should not prove insurmountable. But that will require the military services to double-check and ensure that the standards relate to what the troops are expected to do and not be inflated solely to keep women out of combat.

It also requires that a keen eye be kept on standards, and what yardsticks are used. “This means setting clear standards of performance for all occupations based on what it actually takes to do the job,” said Army General Martin Dempsey, chairman of the Joint Chiefs. “It also means ensuring that these standards are gender-neutral in occupations that will open to women.”

But “gender neutral” can have more than one meaning, according to a December report from the Congressional Research Service:

The use of the term “gender-neutral physical standards” raises questions depending on how it is defined. A plain reading of the term suggests that men and women would be required to meet the same physical standards in order to be similarly assigned. However, in the past, the Services have used this and similar terms to suggest that men and women must exert the same amount of energy in a particular task, regardless of the work that is actually accomplished by either. Hypothetically speaking, if a female soldier carries 70 pounds of equipment five miles and exerts the same effort as a male carrying 100 pounds of equipment the same distance, the differing standards could be viewed as ‘gender-neutral’ because both exerted the same amount of effort, with differing loads.

It’s no small point: the Army notes that troops in Afghanistan sometimes have to carry 127 pounds on their backs. These are definitions that will have to be worked out in the months ahead.

You can glean a lot about how men and women are different by reviewing Pentagon reports since 9/11. Military men are hospitalized more than their female peers for injuries and poisonings, musculoskeletal system/connective tissue disorders, and skin and subcutaneous tissue disorders. Military women were hospitalized more than men for genitourinary disorders, mental disorders, and neoplasms – tumors.

Females in the military also visit the military’s walk-in clinics 50% more often then men do. It’s impossible to know how much of this is because women are more willing to seek help for various maladies rather than having an actually greater number of medical issues. Migraine headaches are three times more common in female than male troops. Military women incur stress fractures at double the rate of their male colleagues.

Differences in how men and women reacted to repeated combat deployments are slight; PTSD levels were similar. Male troops drank more, and females had greater difficulty adjusting once back home.

dod / medical surveillance monthly report

It all goes back to those eye injuries. Hospital visits for eye wounds are double for male military personnel compared to female because of what causes such wounds: “guns/explosives, motor vehicle accidents, and fights or assaults,” according to a Pentagon report.

It’s tough to fight if you can’t see.

The bottom line is that there are differences between men and women in the ranks, just like everywhere else. The Pentagon’s challenge is to accommodate them without watering down the U.S. military’s readiness and lethality.